Extreme ultraviolet lithography, also known as soft x-ray projection lithography, is a contender to replace deep ultraviolet lithography for the manufacture of 0.13 micron, and smaller, minimum feature size semiconductor devices.
However, extreme ultraviolet light, which is generally in the 5 to 40 nanometer wavelength range, is strongly absorbed in virtually all materials. For that reason, extreme ultraviolet systems work by reflection rather than by transmission of light. Through the use of a series of mirrors, or lens elements, and a reflective element, or extreme ultraviolet substrates such as EUV mask blanks, coated with a non-reflective absorber mask pattern, the patterned actinic light is reflected onto a resist-coated semiconductor wafer.
The lens elements and extreme ultraviolet mask blanks of extreme ultraviolet lithography systems are coated with reflective multilayer coatings of materials such as molybdenum and silicon. Reflection values of approximately 65% per lens element, or EUV mask blank, have been obtained by using substrates that are coated with multilayer coatings that strongly reflect light essentially at a single wavelength within an extremely narrow ultraviolet bandpass; e.g., 12 to 14 nanometer bandpass for 13 nanometer ultraviolet light.
Minimum feature size design rules for semiconductor and microelectronics manufacturing continue to shrink with Moore's Law. Use of short wavelength, extreme ultraviolet lithography has the potential to facilitate even smaller design rules although many technical challenges remain to fully commercialize this technology. High-quality, defect-free masks are one critical link the chain. Mask defect inspection generally is expensive and complex.
Thus, a need still remains for an extreme ultraviolet lithography substrate inspection system with simplified optics. In view of growing demands for supporting high-quality and defect-free masks, it is increasingly critical that answers be found to these problems. In view of the ever-increasing commercial competitive pressures, along with growing consumer expectations and the diminishing opportunities for meaningful product differentiation in the marketplace, it is critical that answers be found for these problems. Additionally, the need to reduce costs, improve efficiencies and performance, and meet competitive pressures adds an even greater urgency to the critical necessity for finding answers to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.